#!/usr/bin/env python3
# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
from __future__ import annotations
from contextlib import contextmanager
from typing import Any, Callable, Generator, Optional, TypeVar
from sqlalchemy import create_engine
from sqlalchemy.engine.base import Engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, Session, sessionmaker
# some constants for database fields
HASH_FIELD_LENGTH: int = 32
NAME_OR_TYPE_FIELD_LENGTH: int = 100
LONG_STRING_FIELD_LENGTH: int = 255
JSON_FIELD_LENGTH: int = 4096
# by default, Text gets mapped to a TEXT field in MySQL is 2^16 - 1
# we use have MEDIUMTEXT and LONGTEXT in the MySQL db; in this case, use
# Text(MEDIUMTEXT_BYTES) or Text(LONGTEXT_BYTES). This is preferable to
# using MEDIUMTEXT and LONGTEXT directly because those are incompatible with
# SQLite that is used in unit tests.
MEDIUMTEXT_BYTES: int = 2**24 - 1
LONGTEXT_BYTES: int = 2**32 - 1
# global database variables
SESSION_FACTORY: Optional[Session] = None
# set this to false to prevent SQLAlchemy for automatically expiring objects
# on commit, which essentially makes them unusable outside of a session
# see e.g. https://stackoverflow.com/a/50272761
EXPIRE_ON_COMMIT = False
T = TypeVar("T")
[docs]class SQABase:
"""Metaclass for SQLAlchemy classes corresponding to core Ax classes."""
pass
Base = declarative_base(cls=SQABase)
[docs]def create_mysql_engine_from_creator(
# pyre-fixme[24]: Generic type `Callable` expects 2 type parameters.
creator: Callable,
echo: bool = False,
pool_recycle: int = 10,
**kwargs: Any,
) -> Engine:
"""Create a SQLAlchemy engine with the MySQL dialect given a creator function.
Args:
creator: a callable which returns a DBAPI connection.
echo: if True, set engine to be verbose.
pool_recycle: number of seconds after which to recycle
connections. -1 means no timeout. Default is 10 seconds.
**kwargs: keyword args passed to `create_engine`
Returns:
Engine: SQLAlchemy engine with connection to MySQL DB.
"""
return create_engine(
"mysql://", creator=creator, pool_recycle=pool_recycle, echo=echo, **kwargs
)
[docs]def create_mysql_engine_from_url(
url: str, echo: bool = False, pool_recycle: int = 10, **kwargs: Any
) -> Engine:
"""Create a SQLAlchemy engine with the MySQL dialect given a database url.
Args:
url: a database url that can include username, password, hostname, database name
as well as optional keyword arguments for additional configuration.
e.g. `dialect+driver://username:password@host:port/database`.
echo: if True, set engine to be verbose.
pool_recycle: number of seconds after which to recycle
connections. -1 means no timeout. Default is 10 seconds.
**kwargs: keyword args passed to `create_engine`
Returns:
Engine: SQLAlchemy engine with connection to MySQL DB.
"""
return create_engine(url, pool_recycle=pool_recycle, echo=echo, **kwargs)
[docs]def create_test_engine(path: Optional[str] = None, echo: bool = True) -> Engine:
"""Creates a SQLAlchemy engine object for use in unit tests.
Args:
path: if None, use in-memory SQLite; else
attempt to create a SQLite DB in the path provided.
echo: if True, set engine to be verbose.
Returns:
Engine: an instance of SQLAlchemy engine.
"""
if path is None:
# From SQLALchemy docs:
# "To use a SQLite :memory: database, specify an empty URL:
# `engine = create_engine('sqlite://')`"
# (https://docs.sqlalchemy.org/en/14/core/engines.html#sqlite)
db_path = "sqlite://"
else:
db_path = "sqlite:///{path}".format(path=path)
return create_engine(db_path, echo=echo)
[docs]def init_engine_and_session_factory(
url: Optional[str] = None,
# pyre-fixme[24]: Generic type `Callable` expects 2 type parameters.
creator: Optional[Callable] = None,
echo: bool = False,
force_init: bool = False,
**kwargs: Any,
) -> None:
"""Initialize the global engine and SESSION_FACTORY for SQLAlchemy.
The initialization needs to only happen once. Note that it is possible to
re-initialize the engine by setting the `force_init` flag to True, but this
should only be used if you are absolutely certain that you know what you
are doing.
Args:
url: a database url that can include username, password, hostname, database name
as well as optional keyword arguments for additional configuration.
e.g. `dialect+driver://username:password@host:port/database`.
Either this argument or `creator` argument must be specified.
creator: a callable which returns a DBAPI connection.
Either this argument or `url` argument must be specified.
echo: if True, logging for engine is enabled.
force_init: if True, allows re-initializing engine
and session factory.
**kwargs: keyword arguments passed to `create_mysql_engine_from_creator`
"""
global SESSION_FACTORY
if SESSION_FACTORY is not None:
if force_init:
SESSION_FACTORY.bind.dispose()
else:
return
if url is not None:
engine = create_mysql_engine_from_url(url=url, echo=echo, **kwargs)
elif creator is not None:
engine = create_mysql_engine_from_creator(creator=creator, echo=echo, **kwargs)
else:
raise ValueError("Must specify either `url` or `creator`.")
SESSION_FACTORY = scoped_session(
sessionmaker(bind=engine, expire_on_commit=EXPIRE_ON_COMMIT)
)
[docs]def init_test_engine_and_session_factory(
tier_or_path: Optional[str] = None,
echo: bool = False,
force_init: bool = False,
**kwargs: Any,
) -> None:
"""Initialize the global engine and SESSION_FACTORY for SQLAlchemy,
using an in-memory SQLite database.
The initialization needs to only happen once. Note that it is possible to
re-initialize the engine by setting the `force_init` flag to True, but this
should only be used if you are absolutely certain that you know what you
are doing.
Args:
tier_or_path: the name of the DB tier.
echo: if True, logging for engine is enabled.
force_init: if True, allows re-initializing engine
and session factory.
**kwargs: keyword arguments passed to `create_mysql_engine_from_creator`
"""
global SESSION_FACTORY
if SESSION_FACTORY is not None:
if force_init:
SESSION_FACTORY.bind.dispose()
else:
return
engine = create_test_engine(path=tier_or_path, echo=echo)
create_all_tables(engine)
SESSION_FACTORY = scoped_session(
sessionmaker(bind=engine, expire_on_commit=EXPIRE_ON_COMMIT)
)
[docs]def create_all_tables(engine: Engine) -> None:
"""Create all tables that inherit from Base.
Args:
engine: a SQLAlchemy engine with a connection to a MySQL
or SQLite DB.
Note:
In order for all tables to be correctly created, all modules that
define a mapped class that inherits from `Base` must be imported.
"""
if engine.dialect.name == "mysql" and engine.dialect.default_schema_name == "ax":
raise ValueError(
"The open-source Ax table creation is likely not applicable in this case,"
+ "please contact the Adaptive Experimentation team if you need help."
)
Base.metadata.create_all(engine)
[docs]def get_session() -> Session:
"""Fetch a SQLAlchemy session with a connection to a DB.
Returns:
Session: an instance of a SQLAlchemy session.
"""
global SESSION_FACTORY
if SESSION_FACTORY is None:
init_engine_and_session_factory()
assert SESSION_FACTORY is not None
# pyre-fixme[29]: `Session` is not a function.
return SESSION_FACTORY()
[docs]def get_engine() -> Engine:
"""Fetch a SQLAlchemy engine, if already initialized.
If not initialized, need to either call `init_engine_and_session_factory` or
`get_session` explicitly.
Returns:
Engine: an instance of a SQLAlchemy engine with a connection to a DB.
"""
global SESSION_FACTORY
if SESSION_FACTORY is None:
raise ValueError("Engine must be initialized first.")
return SESSION_FACTORY.bind
[docs]@contextmanager
def session_scope() -> Generator[Session, None, None]:
"""Provide a transactional scope around a series of operations."""
session = get_session()
try:
yield session
session.commit()
except Exception:
session.rollback()
raise
finally:
session.close()
